This invention relates in general to medical monitoring and, more specifically, to cardiopulmonary monitoring.
Congestive heart failure (CHF) is a condition in which the heart is unable to pump enough blood to meet the requirements of the metabolizing tissues in the body, or can do so only at high and ultimately deleterious pressures. Main symptoms are dyspnea (shortness of breath), debilitating fatigue and exertional intolerance. At the advanced stages of CHF the patient is unable to carry out any physical activity without discomfort. Symptoms of heart failure are present even at rest, with increased discomfort upon any level of physical activity. The condition at this stage is inexorably progressive, leading to severe disability and, in the majority of cases, to death.
CHF is currently treated, through the use of drugs, interventional procedures and patient monitoring. Often, a cocktail of drugs is used to lower blood pressure, increase pump efficiency, reduce fluid buildup, limit heart rate, and to thin blood. Interventional procedures include transplants, heart assist devices, valve replacement, angioplasties, stents, and bypass surgery. Patient monitoring may include visits to the doctor's office (averaging 2 to 3 per month), hospital admissions (usually 3 to 4 per year), frequent phone calls to the patient's home by office staff, nurse home visits, home weight checks and home EKG's. Fundamental shortcomings of the current treatment approach are: great demands on physician time, inefficient “fine tuning” of the drug regiment, insufficient patient data collection which are spread far apart and associated high costs.
A tool for evaluating the effect that the above treatment protocols have on a CHF patient is an apparatus called the “metabolic cart.” The metabolic cart measures “peak oxygen (O2) consumption” and CO2 output. This method, also known as spirometry, measures O2 consumption, either during resting states or during dynamic exercise (exercise spirometry), to evaluate and quantify by volume calibration, various basic lung volume and expired gas changes under stress effort conditions. These measurements include minute ventilation, tidal volume, inspiratory/expiratory capacity, functional vital capacity, inspiratory reserve, expiratory reserve, respiratory rate, and maximum voluntary ventilation. In addition, mercury-in-silastic strain gauge plethysmography has been used both experimentally and clinically to evaluate breathing patterns in patients with lung disease, sleep apnea, or congestive heart failure, who may present with respiratory trends of periodic breathing or Cheyne-Stokes patterns.
Results from the measurements help evaluate patient status, adjust treatment protocols and improve quality of life. The measurements are also used as a tool for monitoring heart failure deterioration and mortality. In particular, peak O2 consumption is the cornerstone of the cardiac evaluation to determine who is in need of heart transplantation. However, despite their power and usefulness in managing CHF patients, peak O2 consumption measurements are expensive, difficult to carry out and remain largely the domain of research laboratories and CHF specialty clinics.
Even with recent advances in CHF management and improved survival in coronary artery disease and hypertension, CHF mortality has increased fourfold over the last 25 years. Given its increasing prevalence and profound cost in treatment, CHF is a major public health problem. Heart Failure is the leading cause of hospital admission in the USA, accounting for 600,000 admissions per year. There are twice as many admissions for heart failure alone than for all other cardiovascular disease combined. This number continues to increase. Contributing to the increasing cost of CHF is the management aspect, which is physician and time intensive.
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